Many orthopaedic procedures involve the implantation of prosthetic devices to replace badly damaged or diseased bone tissue. Common orthopaedic procedures that involve prosthetic devices include total or partial hip, knee and shoulder replacement. Hip replacement involves total or partial replacement of the hip ball and socket joint.
A total hip replacement procedure typically involves the implantation of two main component systems: the femoral component and an acetabular component. The femoral component includes a rigid stem that is anchored within the existing femur and also includes a head that replaces the natural hip joint femoral head. The acetabular component is secured within the acetabulum of the patient and serves as a bearing surface for the head of the femoral component.
Historically, acetabular components have a generally rounded outer surface that is secured to natural bone within the acetabulum and include a roughly hemispherical interior surface for receiving a round femoral head. The femoral head and hemispherical interior surface form a ball and socket joint that approximates the natural hip joint. The acetabular component often includes an outer shell and one or more intermediate components, or liners. The outer shell is anchored or otherwise secured to the bone tissue within the acetabulum and the liner or liners are disposed within the outer shell. The liner(s) form the bearing surface for the pivoting femoral head.
Regardless of the precise structure, prior art hip prostheses typically employ the ball and socket or spherical rotation joint to approximate anatomical hip movement.
A set of problems associated with hip prosthesis arises from the wear of the hip implant bearings. In particular, extensive use of a prosthetic hip can cause the bearings to wear, releasing debris in and around the surrounding tissue. For example, a typically total hip prosthesis includes a metal or ceramic outer shell, an ultra high molecular weight polyethylene (UHMWPE) liner, and a cobalt-chromium or ceramic femoral head. In such a prosthesis, it has been observed that the bearing surface of the UHMWPE liner wears, thereby producing particulate debris.
Particulate from UHMWPE wear can interfere with the motion capabilities of the prosthetic and furthermore can create an adverse biological reaction. Small debris can produce osteolysis (bone resorption) and/or cause an immune response.
Similarly, if a metal liner is instead used, the wear from the metal on metal bearings (metal liner to metal femoral head) can release increased levels of metal ions in the body which can produce adverse health effects. Ceramic liners do not produce metal ions, but are expensive and can fail in a brittle manner, which is highly undesirable.
Accordingly, there exists a need for reducing the adverse affects caused by wear of the bearing surfaces of total hip replacement prostheses.